The early 1970's created a considerable growth period for both mini-computers and mainframe computers. These type of computers, at that time, were mostly invulnerable to improper access by unauthorized users since they were installed, at least for the most part, in high security computer room environments. However, during the 1980's, the rapid growth of desktop systems, including the many models of IBM-compatible Personal Computers, contributed to open up a whole new domain of computer systems including interconnected world-wide networks which are now in operation. At present, all three "levels" of technology such as the PC's, Mini's and Mainframe computers are networked together. This has resulted in malicious codes, such as viri, being able to create extreme problems for two components of these interconnected systems, i.e. (1) the system central processor(s) and memory: and (2) the system storage devices.
Examination of damage caused by viri and other malicious codes indicates that it is the system storage devices, in particular, which can be the most severely damaged by malicious codes or unauthorized modifications. This is the area where all "data" resides which includes all the user application data (e.g. the database information, financial information, institutional records, etc.); all the application software programs (e.g. the database software, financial software, records management software, etc.) and even the operating system software itself such as MS-DOS. A single incident of contamination by a malicious code may totally erase or render useless any storage device (the previously mentioned second component) of its data in a manner so as to prevent even the most knowledgeable programmer being able to recover that data.
Malicious codes can also contaminate the system's central processor and memory (the first-mentioned component). However, in most cases, a simple power OFF or RESET will totally eradicate any malicious codes from these type of storage locations.
Practically all data storage devices, other than a Compact Disk ROM, are "read and write" devices. Therefore, one of the items desired is the ability to effectively prevent the write function whenever and wherever a computer's operational needs do not require the write function. That ability to prevent the write function should also have the capability of being accomplished in a manner that system operators and users can easily understand so that the level of protection will be effectively increased. In some applications, it may also be desirable to be able to prevent "read" access as well in particular areas that may require some limitation to the specific operating system or application system software for reasons of "restricting functionally" to only authorized tasks.
Many of the magnetic (tape or disk) storage devices have offered some kind of ability for "turning OFF" the "write" function. Large mainframe computers have used secondary memory devices in the form of tape and disk drives with it being quite usual to perform an operation which results in "reading" from one device and "writing" into another device at the same time. In these cases, the tape drives and disk drives have built-in circuits and a "write protect" switch at the hardware level that, by activation, prevents any accidental loss of data or corruption of program material while an operator is performing routine operating procedures. Built-in write protection has also been a standard feature on many mini-computers which enables an operator to quickly and totally protect program material from being lost or adulterated during some part of an operating procedure where a mishap might occur. This type of feature, however, has not been generally available on the majority of desktop computers. Furthermore, this type of feature does not include all the desired functions that are presently required. Some manufacturers have included a hard disk power OFF switch on Personal Computers but this feature has only been seen in laptops where battery conservation was the motive.
A "write protect" device also exists for floppy disk technology wherein the "write protect" device takes the form of a notch in a floppy disk's case, which notch can be covered with a removable adhesive tab (5.25" floppy) or a slider within the case of a 3.5" floppy disk to protect any data stored on that floppy disk. The floppy disk drive can sense (optically or mechanically) whether or not that notch is covered by the tab and, as a result, decide if that disk is "write protected". This technique will only guard against accidents in the nature of over-writing valuable data stored on a floppy disk.
A known write protect control circuit for computer's hard disk systems is described in U.S. Pat. No. 4,734,851. That circuit in U.S. Pat. No. 4,734,851 has data buses connected between a disk controller and two disk drive systems, which drives are also connected to the disk controller via a common control bus. That common control bus includes a first device "select wire" to select a first disk drive device and a second device "select wire" to select a second disk drive device. Only one of these device "select wires" can be selected (activated) at any one time by the disk controller to place one of the disk drives in a standby mode. That common control bus also includes a "write fault" wire which can be activated by either of the disk systems whenever a selected disk system cannot accept data being sent to it. Activation of the "write fault" wire informs the controller that the data was not written as requested. A "write gate" wire is also provided in the common control bus which provides a "write gate" enable signal whenever data is to be recorded on a selected disk. These are all common features which normally exist in personal computers. However, as described in U.S. Pat. No. 4,734,851, a "write protect" device is inserted in the "write gate" wire between the controller and disk drive devices with that "write protect" device being connected to both "device select" wires and the "write fault" wire of the common control bus. A switch associated with the "write protect" device can be activated to prevent any "write gate" enable signal from being applied to a selected disk drive device when that device is to be protected, i.e. when the switch is placed in a "protected mode" position. However, the "write protect" device will allow a "write gate" enable signal to be applied to a selected disk drive device when that device is unprotected with the switch being in the other "unprotected" position. When the "write protect" device prevents a "write gate" enable signal from reaching a selected disk drive, it also applies a signal to the "write fault" wire to inform the controller that no data has been recorded as requested by the controller. This type of "write protect" device only allows for a limited number of protective functions.